Waveguide assembly with virtual image focus

ABSTRACT

An optical combiner, configured for use in a mixed-reality display system that combines holographic and real-world images, includes an assembly of see-through waveguides that are arranged in a stack to provide full color holographic images from constituent RGB (red, green, and blue) color components received from a holographic image source. Each waveguide—one per RGB color component—includes an in-coupling DOE (diffractive optical element), an intermediate DOE, and an out-coupling DOE that are disposed on internal surfaces of the stacked waveguides in the optical combiner. Each of the out-coupling DOEs incorporates a diffractive lens functionality to render the out-coupled holographic images at a set depth on the mixed-reality display. In an illustrative non-limiting example, the out-coupling DOE may provide a half diopter of negative lens power to set the optical focus of the holographic images at 1.33 m.

BACKGROUND

Mixed-reality computing devices, such as head-mounted display (HMD)systems and handheld mobile devices (e.g. smart phones, tabletcomputers, etc.), may be configured to display information to a userabout virtual objects, such as holographic images, and/or real objectsin a field of view of the user and/or a field of view of a camera of thedevice. For example, an HMD device may be configured to display, using asee-through display system, virtual environments with real-world objectsmixed in, or real-world environments with virtual objects mixed in.Similarly, a mobile device may display such information using a cameraviewfinder window.

SUMMARY

An optical combiner, configured for use in a mixed-reality displaysystem that combines holographic and real-world images, includes anassembly of see-through waveguides that are arranged in a stack toprovide full color holographic images from constituent RGB (red, green,and blue) color components received from a holographic image source.Each waveguide—one per RGB color component—includes an in-coupling DOE(diffractive optical element), an intermediate DOE, and an out-couplingDOE that are disposed on internal surfaces of the stacked waveguides inthe optical combiner. The in-coupling DOEs in-couple collimatedholographic image light as RGB color component inputs to the respectivewaveguides. The intermediate DOEs expand the exit pupil of the imagelight in a first direction and the out-coupling DOEs provide pupilexpansion in a second direction relative to the input while out-couplingthe holographic images to a system user's eye. Each of the out-couplingDOEs incorporates a diffractive lens functionality to render theout-coupled holographic images at a set depth on the mixed-realitydisplay. In an illustrative non-limiting example, the out-coupling DOEmay provide a half diopter of negative lens power to set the opticalfocus of the holographic images at 1.33 m.

The out-coupling DOEs on the waveguides are each configured withlocally-modulated grating feature periods to transform the planarwavefront of the collimated holographic images provided as an the inputof the optical combiner to a spherical wavefront with a radius ofcurvature that matches the set depth of optical focus. The localmodulation of grating period is implemented using curved grating linesin which the period changes across the out-coupling DOE are kept smallrelative to an unmodulated configuration. Such approach advantageouslyminimizes the effects of spectral dispersion to reduce distortion of thedisplayed holographic images and the real-world images that are seenthrough the out-coupling DOE.

Some waveguide-based mixed-reality display systems known in the opticalarts employ a set of lenses that provide for virtual image focus at aset distance using a negative lens on the eye side of an opticalcombiner and its conjugate positive lens on the real-world side. Thelenses may be incorporated into protective elements, such as a visor,that externally encase the combiner to protect the optical elementsduring system use and handling. By locating the DOEs on the internalsurface of stacked waveguides in the optical combiner of the presentwaveguide assembly and configuring the out-coupling DOE as a diffractivenegative lens, such lenses and external protective elements can beeliminated from the display system design which may reduce parts count,cost, size, and weight. Such reductions can be particularlyadvantageous, for example, when the mixed-reality display system is usedin head-mounted display (HMD) display applications and in consumermarkets where cost sensitivity may be heightened. In addition, opticalperformance of the mixed-reality display system may be enhanced by theelimination of the lenses and protective elements by increasingsee-through transmission, uniformity, and contrast and by reducing ghostimages, reflections, and other aberrations caused by the lenses and/orprotective elements.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter. Furthermore, the claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in any part ofthis disclosure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an illustrative near-eye display system;

FIG. 2 shows propagation of light in a waveguide by total internalreflection (TIR);

FIG. 3 shows a view of an illustrative exit pupil expander;

FIG. 4 shows illustrative collimated light output from a diffractiveoptical element (DOE) in an exit pupil expander;

FIG. 5 shows a view of an illustrative exit pupil expander in which theexit pupil is expanded along two directions of the field of view (FOV);

FIG. 6 shows an illustrative input to an exit pupil expander in whichthe FOV is described by angles in horizontal, vertical, or diagonalorientations;

FIG. 7 illustratively shows holographic images from a virtual world thatare overlaid onto real-world images within a field of view (FOV) of amixed-reality head-mounted display (HMD) device;

FIGS. 8A, 8B, and 8C show illustrative paths of light rays that arerespectively associated with a distant object, an object at infinity,and a nearby object;

FIG. 9 shows an illustrative negative lens that provides for a virtualimage that is located at a focal point of the lens;

FIG. 10 shows a combination of a positive and negative lens that arelocated on either side of a waveguide and out-coupling DOE;

FIG. 11 shows an illustrative waveguide and out-coupling DOE arranged tooutput non-collimated diverging optical beams to provide virtual imagefocus;

FIGS. 12A, 12B, and 12C show illustrative wavefronts that arerespectively associated with a distant object, an object at infinity,and a nearby object;

FIG. 13 shows an illustrative unmodified out-coupling DOE without localmodulation of grating features;

FIG. 14 shows an illustrative out-coupling DOE that is modified withlocal modulation of grating features to output non-collimated divergingoptical beams and provide virtual image focus;

FIG. 15 is an illustrative diagram pertaining to calculations totransform a central holographic image pixel;

FIG. 16 is an illustrative diagram pertaining to calculations to shift agrating feature;

FIGS. 17 and 18 are illustrative diagrams pertaining to calculations toshift a grating feature at any given location on an out-coupling DOE;

FIG. 19 is an enlarged plan view of an illustrative out-coupling DOEthat shows the period of every 2000^(th) grating feature being modulatedto provide for virtual image focus at 1.33 m;

FIG. 20 is an enlarged plan view of an illustrative out-coupling DOEthat shows the period of every 2000^(th) grating feature being modulatedto provide for virtual image focus at 0.5 m;

FIG. 21 shows a side view of an illustrative assembly of threewaveguides with integrated DOEs that are stacked to form an opticalcombiner, in which each waveguide handles a different color in an RGB(red, green, blue) color model, and in which the DOEs are disposed oninternal surfaces of the waveguides in the optical combiner;

FIG. 22 shows illustrative propagation of holographic image lightthrough an optical combiner;

FIG. 23 is a flowchart of an illustrative method for providing awaveguide assembly with virtual image focus;

FIG. 24 shows an illustrative arrangement of diffractive opticalelements (DOEs) configured for in-coupling, exit pupil expansion in twodirections, and out-coupling;

FIG. 25 shows a profile of a portion of an illustrative diffractiongrating that has straight gratings;

FIG. 26 shows a profile of a portion of an illustrative diffractiongrating that has asymmetric or slanted gratings;

FIG. 27 shows a pictorial front view of an illustrative sealed visorthat may be used as a component of an HMD device;

FIG. 28 shows a pictorial rear view of an illustrative sealed visor;

FIG. 29 shows a partially disassembled view of an illustrative sealedvisor;

FIG. 30 is a pictorial view of an illustrative example of avirtual-reality or mixed-reality HMD device that may use the presentwaveguide assembly with virtual image focus;

FIG. 31 shows a block diagram of an illustrative example of avirtual-reality or mixed-reality HMD device that may use the presentwaveguide assembly with virtual image focus; and

FIG. 32 shows a block diagram of an illustrative electronic device thatincorporates a mixed-reality display system that may use the presentwaveguide assembly with virtual image focus.

Like reference numerals indicate like elements in the drawings. Elementsare not drawn to scale unless otherwise indicated.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of an illustrative near-eye display system100 which may incorporate an imager 105 and an optical system 110. Theoptical system 110 may also include imaging optics 120 (e.g., magnifyingand/or collimating lenses), and an optical combiner 125 that providesexit pupil expander (EPE) functionality that may be implemented using atleast one waveguide 130.

Multiple diffractive optical elements (DOEs, also synonymously referredto as diffraction gratings) are disposed on the waveguide 130 andconfigured to provide in-coupling of incident light into the waveguide,exit pupil expansion in two directions, and out-coupling of light out ofthe waveguide to an eye 115 of a system user. Near-eye display systemsare often used, for example, in head-mounted display (HMD) devices inindustrial, commercial, and consumer applications. Other devices andsystems may also use near-eye display systems, as described below. Thenear-eye display system 100 is an example that is used to providecontext and illustrate various features and aspects of the presentwaveguide assembly with virtual focus.

The imager 105 in system 100 may include one or more sources ofholographic images (e.g., images representing objects from a virtualworld that are not necessarily stereo images) that interoperate with theoptical system 110 to deliver virtual images as a virtual display to auser's eye 115 (it is noted that the terms holographic image, virtualimage, and virtual object are utilized as synonyms unless statements orcontext indicate otherwise). The imager 105 may include, for example,RGB (red, green, blue) light emitting diodes (LEDs), LCOS (liquidcrystal on silicon) devices, OLED (organic light emitting diode) arrays,MEMS (micro-electro mechanical system) devices, or any other suitabledisplays or micro-displays operating in transmission, reflection, oremission. The imager may also include electronics such as processors,optical components such as mirrors and/or lenses, and/or mechanical andother components that enable a virtual display to be composed andprovide one or more input optical beams to the optical system.

In a near-eye display system the imager does not actually shine theimages on a surface such as a glass lens to create the visual displayfor the user. This is not feasible because the human eye cannot focus onsomething that is that close. Rather than create a visible image on asurface, the near-eye display system 100 uses the optical system to forma pupil and the eye 115 acts as the last element in the optical chainand converts the light from the pupil into an image on the eye's retinaas a virtual display. It may be appreciated that the exit pupil is avirtual aperture in an optical system. Only rays which pass through thisvirtual aperture can exit the system. Thus, the exit pupil describes aminimum diameter of the holographic image light after leaving thedisplay system. The exit pupil defines the eyebox which comprises aspatial range of eye positions of the user in which the holographicimages projected by the display system are visible.

The waveguide 130 facilitates light transmission between the imager andthe eye. One or more waveguides can be utilized in the near-eye displaysystem because they are transparent and because they are generally smalland lightweight (which is desirable in applications such as HMD deviceswhere size and weight are generally sought to be minimized for reasonsof performance and user comfort). For example, the waveguide 130 canenable the imager 105 to be located out of the way, for example, on theside of the user's head or near the forehead, leaving only a relativelysmall, light, and transparent waveguide optical element in front of theeyes.

In an illustrative implementation, the waveguide 130 operates using aprinciple of total internal reflection (TIR), as shown in FIG. 2, sothat light can be coupled among the various optical elements in thesystem 100. TIR is a phenomenon which occurs when a propagating lightwave strikes a medium boundary (e.g., as provided by the opticalsubstrate of a waveguide) at an angle larger than the critical anglewith respect to the normal to the surface. In other words, the criticalangle (θ_(c)) is the angle of incidence above which TIR occurs, which isgiven by Snell's Law, as is known in the art. More specifically, Snell'slaw specifies that the critical angle (θ_(c)) is specified using thefollowing equation:

θ_(c)=sin⁻¹(n2/n1)

where θ_(c) is the critical angle for two optical mediums (e.g., thewaveguide substrate and air or some other medium that is adjacent to thesubstrate) that meet at a medium boundary, n1 is the index of refractionof the optical medium in which light is traveling towards the mediumboundary (e.g., the waveguide substrate, once the light is coupledtherein), and n2 is the index of refraction of the optical medium beyondthe medium boundary (e.g., air or some other medium adjacent to thewaveguide substrate).

FIG. 3 shows a view of an illustrative EPE 305 that uses separate leftand right displays (300 _(L) and 300 _(R)), each with its own imager(105 _(L) and 105 _(R)) and imaging optics (120 _(L) and 120 _(R)). Theillustrative EPE is provided as an element of an optical combiner, asdiscussed below in the text accompanying FIG. 21. Each display in theEPE receives one or more input optical beams from an imager 105 as anentrance pupil for holographic image light to produce one or more outputoptical beams with expanded exit pupil in one or two directions relativeto the input. The expanded exit pupil typically facilitates a virtualdisplay to be sufficiently sized to meet the various designrequirements, such as eyebox size, image resolution, field of view(FOV), and the like, of a given optical system while enabling the imagerand associated components to be relatively light and compact.

The EPE 305 is configured, in this illustrative example, to providebinocular operation for both the left and right eyes which may supportbinocular or stereoscopic viewing. Some components that may be utilizedfor binocular or stereoscopic operation such as scanning mirrors,lenses, filters, beam splitters, MEMS (micro-electromechanical system)devices, or the like are not shown in FIG. 3 for sake of clarity inexposition. The EPE 305 utilizes two out-coupling DOEs, 310 _(L) and 310_(R) that are supported on the waveguides 130 _(L) and 130 _(R) and twoin-coupling DOEs 340 _(L) and 340 _(R).

The in-coupling and out-coupling DOEs may be configured using multipleDOEs and may further include one or more intermediate DOEs (not shown)as described below. The DOEs may be arranged in various configurationson the waveguide, for example, on the same side or different sides andmay further be single- or double-sided. While the EPE 305 is depicted ashaving a planar configuration, other shapes may also be utilizedincluding, for example, curved or partially spherical shapes, in whichcase gratings in the DOEs disposed thereon may be non-co-planar.

As shown in FIG. 3, exemplary output beams 350 from the EPE 305 areparallel to the exemplary input beams 355 that are output from theimager 105 to the in-coupling DOE 340. In some implementations, theinput beams are collimated such that the output beams are alsocollimated, as indicated by the parallel lines in the drawing.Typically, in waveguide-based combiners, the input pupil needs to beformed over a collimated field, otherwise each waveguide exit pupil willproduce an image at a slightly different distance. This results in amixed visual experience in which images are overlapping with differentfocal depths in an optical phenomenon known as focus spread. Asdiscussed in more detail below, the collimated inputs and outputs inconventional waveguide-based display systems provide holographic imagesdisplayed by the optical system 110 that are focused at infinity, asindicated by reference numeral 405 in FIG. 4.

As shown in FIG. 5, the EPE 305 may be configured to provide an expandedexit pupil in two directions (i.e., along each of a first and secondcoordinate axis). As shown, the exit pupil is expanded in both thevertical and horizontal directions. It may be understood that the terms“left,” “right,” “up,” “down,” “direction,” “horizontal,” and “vertical”are used primarily to establish relative orientations in theillustrative examples shown and described herein for ease ofdescription. These terms may be intuitive for a usage scenario in whichthe user of the near-eye display device is upright and forward facing,but less intuitive for other usage scenarios. The listed terms are notto be construed to limit the scope of the configurations (and usagescenarios therein) of near-eye display features utilized in the presentarrangement.

The entrance pupil to the EPE 305 at the in-coupling DOE 340 isgenerally described in terms of field of view (FOV), for example, usinghorizontal FOV, vertical FOV, or diagonal FOV as shown in FIG. 6. TheFOV is typically a parameter of interest that can vary by application.For example, an HMD device for one application may be designed with adiagonal FOV of 34 degrees for holographic images while another may havea 52-degree FOV. Some non-planar waveguide-based HMD devices have beenproposed with FOVs of more than 70 degrees. It is noted that FOV is justone of many parameters that are typically considered and balanced by HMDdesigners to meet the requirements of a particular implementation. Forexample, such parameters may include eyebox size, brightness,transparency and duty time, contrast, resolution, color fidelity, depthperception, size, weight, form-factor, and user comfort (i.e., wearable,visual, and social), among others.

FIG. 7 shows an illustrative mixed-reality HMD device 705 worn by a user710 having a see-through waveguide display 715 that incorporates thenear-eye display system 100 (FIG. 1), among various other components andmay be further adapted to provide virtual image focus in accordance withthe principles discussed herein. As noted above, an imager (not shown)generates holographic images that are guided by the waveguide display tothe user. Being see-through, the waveguide display enables the user toperceive light from the real world.

The see-through waveguide display 715 can render holographic images ofvarious virtual objects that are superimposed over the real-world imagesthat are collectively viewed using the see-through waveguide display tothereby create a mixed-reality environment 700 within the HMD device'sFOV 720. It is noted that the FOV of the real world and the FOV of theholographic images from the virtual world are not necessarily identical,as the FOV of the near-eye display system 100 is typically a subset ofthat associated with the real-world FOV.

In this illustrative example, the user 710 is physically walking in areal-world urban area that includes city streets with various buildings,stores, etc., with a countryside in the distance. The FOV of thecityscape viewed on HMD device 705 changes as the user moves through thereal-world environment and the device can render static and/or dynamicvirtual images over the real-world view. In this illustrative example,the holographic images include a tag 725 that identifies a restaurantbusiness and directions 730 to a place of interest in the city. Themixed-reality environment 700 seen visually on the waveguide display mayalso be supplemented by audio and/or tactile/haptic sensations producedby the HMD device in some implementations.

During natural viewing, the human visual system relies on multiplesources of information, or “cues,” to interpret three-dimensional shapesand the relative positions of objects. Some cues rely only on a singleeye (monocular cues), including linear perspective, familiar size,occlusion, depth-of-field blur, and accommodation. Other cues rely onboth eyes (binocular cues), and include vergence (essentially therelative rotations of the eyes required to look at an object) andbinocular disparity (the pattern of differences between the projectionsof the scene on the back of the two eyes).

To view objects clearly, humans must accommodate, or adjust their eyes'focus, to the distance of the object. At the same time, the rotation ofboth eyes must converge to the object's distance to avoid seeing doubleimages. In natural viewing, vergence and accommodation are linked. Whenviewing something near (e.g. a housefly close to the nose) the eyescross and accommodate to a near point. Conversely, when viewingsomething at optical infinity, the eyes' lines of sight become paralleland the eyes' lenses accommodate to infinity.

In typical HMD devices, users will always accommodate to the focaldistance of the display (to get a sharp image) but converge to thedistance of the object of interest (to get a single image). When usersaccommodate and converge to different distances, the natural linkbetween the two cues must be broken and this can lead to visualdiscomfort or fatigue. Accordingly, to maximize the quality of the userexperience and comfort with the HMD device 705 (FIG. 7), holographicimages may be rendered in a plane to appear at a constant distance fromthe user's eyes. For example, holographic images, including the images725 and 730, can be set at a fixed depth of 1.33 m from the user 710.Thus, the user 710 will always accommodate near 1.33 m to maintain aclear image in the HMD device. It may be appreciated that 1.33 m is anillustrative distance and is intended to be non-limiting. Otherdistances may be utilized to meet requirements of specific applications.For example, 2 m has been specified as a fixed depth for holographicimages in some mixed-reality HMD device applications with satisfactoryresults.

In the real world as shown in FIG. 8A, light rays 805 from distantobjects 810 reaching an eye 115 of a user are almost parallel.Real-world objects at optical infinity (roughly around 6 m and fartherfor normal vision) have light rays 820 that are exactly parallel whenreaching the eye, as shown in FIG. 8B. Light rays 825 from a nearbyreal-world object 830 reach the eye with different, more divergentangles, as shown in FIG. 8C, compared to those for more distant objects.

Various approaches may be utilized to render holographic images with thesuitable divergent angles to thereby appear at the targeted depth offocus. To illustrate the principles of the present waveguide displaywith virtual image focus, a brief discussion of one particularillustrative known technique is now provided.

FIG. 9 shows that a concave lens 905 can diverge the collimated/parallelrays 950 (e.g., beams 350 shown in FIG. 3) that are received from aconventional out-coupling DOE (not shown) to produce an optical virtualimage having a location that is apparent to the user at a focal point, F(as indicated by reference numeral 915), that is determined by the focallength of the lens (e.g., 0.5 m, 1.33 m, 2 m, etc.). The rays from theconcave lens arriving at the user's eye 115 are non-parallel anddivergent, as shown, and converge using the eye's internal lens to formthe image on the retina, as indicated by reference numeral 920.

A pair of lenses may be utilized to provide virtual image focus at a setdepth with a conventional waveguide display, as shown in FIG. 10 (forclarity in exposition, the holographic image source and other opticalcomponents used to handle the images in the waveguide 130 are notshown). With this illustrative approach, a negative (i.e., concave) lens1005 is located on the eye side (indicated by reference numeral 1010) ofthe waveguide 130. The negative lens acts over the entire extent of theeyebox associated with the user's eye 115 to thereby create thediverging rays 1015 from the collimated rays 950 that exit theout-coupling DOE 310. To ensure that the user's view of the real worldremains unperturbed by the negative lens, a conjugate positive (i.e.,convex) lens 1020 is located on the real-world side (indicated byreference numeral 1025) of the waveguide to compensate for the impact ofthe negative lens on the real-world view.

While the lenses 1005 and 1020 can perform satisfactorily to implementvirtual image focus at a set depth in many applications, it may beadvantageous in other applications to implement and utilize analternative virtual image focus approach. FIG. 11 shows an illustrativewaveguide 1100 on which an out-coupling DOE 1105 is disposed. Theout-coupling DOE is specifically adapted to output non-collimateddiverging optical beams 1110 to the user's eye 115 to thereby presentholographic images at a predetermined focal depth range without the useof external lenses. In addition to providing virtual image focus, theout-coupling DOE 1105 is also configured to incorporate an exit pupilexpansion functionality, as discussed above.

The out-coupling DOE 1105 incorporates negative lens functionality, forexample, having −0.5 diopters of optical power to provide for a focalplane for the rendered holographic images located at 2 m in front of theuser. Different amounts of optical power may be utilized to provide forfocal planes that are located at other distances to suit requirements ofa particular application. The lens power of the out-coupling DOE doesnot affect the zeroth diffraction order that travels in TIR down thewaveguide 1100 (i.e., from top to bottom in the drawings), but insteadonly the diffracted out-coupled field. In addition, the see-throughfield is not affected by the negative lensed out-coupling DOE becausewhatever portion of the see-through field that is diffracted by theout-coupling DOE is trapped by TIR in the waveguide and is therefore nottransmitted to the user's eye 115. Thus, by introducing the negativeoptical power to the out-coupling DOE, neither of the lenses 1005 and1020 shown in FIG. 10 will be needed to impart virtual image focus at apredetermined non-infinite focal depth (as indicated by referencenumeral 1115).

The out-coupling DOE 1105 is adapted to incorporate the negative lens inview of the observation that the wave nature of light provides forspherical wavefronts. As shown in FIG. 12A, a distant object 1205 willhave wavefronts 1210 that each have a particular radius of curvature.When an object is located at infinity, as shown in FIG. 12B, each of thespherical wavefronts 1215 has an infinite radius of curvature. Theradius of curvature of each spherical wavefront 1220 decreases for anearby object 1225 as shown in FIG. 12C. Therefore, manipulation of theconfiguration of the gratings in the out-coupling DOE to thereby impacta spherical shape to the wavefronts of the diffracted fields may beexpected to provide a sufficient negative optical power to the DOE toeliminate the requirement for external lenses.

A simplified grating equation for the first negative (i.e., −1)diffractive order is

${\sin\;\theta_{- 1}} = {{n\;\sin\;\theta_{in}} - \frac{\lambda}{d}}$

where d is the grating period (i.e., distance between successivefeatures, e.g., gratings, grooves/lines) for the out-coupling DOE 1105,as shown in FIG. 13. Equation (1) demonstrates that the angle ofdiffraction can be tuned by locally changing the grating period (alongwith the orientation when working in three dimensions).

As shown in FIG. 14, a shift in grating features of the out-coupling DOE1105 from an original location 1405 to a shifted location 1410 willresult in a change of phase of a diffracted field in accordance with thedetour phase principle introduced by Brown and Lohmann to simulatewavefront propagation in computer-generated holograms using Fouriertransformations. Under this principle, the modulation of local positionof grating features in the out-coupling DOE will change the phase frontof the diffracted field from planar to spherical.

FIG. 15 is an illustrative diagram 1500 pertaining to calculations totransform a central holographic image pixel. With reference to thedrawing, consider diffraction of the center pixel at position x, y, z=0,we wish to change the local period such that the light diffracts intothe direction of the unit vector:

s = s_(x)x + s_(y)y + s_(z)z${{{where}\mspace{14mu} s_{x}} = \frac{x}{r}},{s_{y} = \frac{y}{r}},{{{and}\mspace{14mu} s_{z}} = {- \frac{f}{r}}},{{{and}\mspace{14mu} r} = {\sqrt{x^{2} + y^{2} + f^{2}}.}}$

The wave vector thus takes the form

$k_{0} = \frac{2\pi}{\lambda_{0}}$

and λ₀ is the design wavelength. The original pixel propagates in thedirection k_(ox)=0, k_(oy)=0, k_(oz)=−k₀. We thus just have to find alocal period and orientation that makes the desired change.

Now the incoming 0 pixel inside the waveguide propagates in thedirection given by k_(inx)=D_(ox), k_(iny)=D_(oy) where D_(ox) andD_(oy) denote the x and y components of the original grating vector andwe have chosen the out-coupled diffractive order to be −1. That is,after the change of the grating we have

$\begin{matrix}{{{k_{x} = {{k_{inx} - D_{x}} = {D_{ox} - D_{x}}}},{k_{y} = {{k_{iny} - D_{y}} = {D_{oy} - {D_{y}.{Hence}}}}}}{{D_{x} = {D_{ox} - \frac{k_{0^{x}}}{r}}},{D_{y} = {D_{oy} - {\frac{k_{0}y}{r}.}}}}} & {{Eq}.\mspace{11mu}(1)}\end{matrix}$

Now the local period and orientation is obtained from:

${d = \frac{2\pi}{\sqrt{D_{x}^{2} + D_{y}^{2}}}},{\phi = {\arctan( \frac{D_{y}}{D_{x}} )}}$

The shift Δ of the grating lines causes a phase change

$\Phi = \frac{2\pi\Delta}{d_{o}}$

in the −1 diffraction order in which the shift takes place in thedirection of the original grating vector. Demanding that the phaseequals that of a diverging spherical wave with an origin at the focalpoint, we have

$D_{o} = \frac{2\pi}{d_{o}}$${d_{ox} = {d_{o}\sec\phi_{o}}},{d_{oy} = {d_{o}csc\phi_{o}}},{D_{ox} = {{D_{o}\cos\phi_{o}} = {2{\pi/d_{ox}}}}},{D_{oy} = {{D_{o}\sin\phi_{o}} = \frac{2\pi}{d_{oy}}}}$

as shown in the illustrative diagram 1600 shown in FIG. 16.

As shown in the illustrative diagram 1700 in FIG. 1700, for the shift Δwe have Δ_(x)=Δsecϕ_(o) and Δ_(y)=Δcscϕ_(o), that is

$\frac{\Delta}{d_{o}} = {\frac{\Delta}{d_{ox}} = \frac{\Delta}{d_{oy}}}$

where the shift is an integrated/cumulative quantity.

The components of the local period are obtained from:

${d_{x} = {d_{ox} + {d_{x}\frac{\partial\Delta_{x}}{\partial x}}}},{d_{y} = {d_{oy} + {d_{y}\frac{\partial\Delta_{y}}{\partial y}}}}$

which gives at once

${D_{x} = {D_{ox}( {1 - \frac{\partial\Delta_{x}}{\partial x}} )}},{D_{y} = {{D_{oy}( {1 - \frac{\partial\Delta_{y}}{\partial y}} )}.}}$

Partial differentiations are straightforward since

$\frac{\partial r}{\partial x} = {{\frac{x}{r}\mspace{14mu}{and}\mspace{14mu}\frac{\partial r}{\partial y}} = \frac{y}{r}}$

For example, we have

$\frac{\partial\Delta_{x}}{\partial x} = {{\frac{k_{0}}{D_{ox}}\frac{\partial r}{\partial x}} = \frac{k_{0}x}{D_{ox}r}}$

and thus obtain

${D_{x} = {D_{ox} - \frac{k_{o}x}{r}}},{D_{y} = {D_{oy} - \frac{k_{0}y}{r}}}$

which is exactly the same expression in Equation (1) above that wasderived using only the propagation direction of the out-coupleddiffraction order.

It is noted that Δ is the realized shift at any given location (x, y).If we want to know how much a particular grating line must be shifted,we must solve for it. Let us denote Δ′ as the unknown shift. Working inthe coordinates denoted by primes (as shown in diagram 1800 in FIG. 18)we have

${\Delta( {{x^{\prime} + \Delta^{\prime}},y^{\prime}} )} = \frac{d_{o}{k_{o}\lbrack {\sqrt{( {x^{\prime} + \Delta^{\prime}} )^{2} + y^{\prime^{2}} + f^{2}} - f} \rbrack}}{( {2\pi} )}$

This expression must equal Δ′ (x′, y′) which leads to a quadraticequation

${{\Delta^{\prime^{2}}( {\frac{\lambda_{0}^{2}}{d_{0}^{2}} - 1} )} + {\Delta^{\prime}( {\frac{2f\;\lambda_{0}}{d_{0}} - {2x^{\prime}}} )} - x^{\prime} - y^{\prime}} = 0.$

This equation can be readily solved from

$\Delta^{\prime} = {\frac{{- b} \pm \sqrt{b^{2} - {4ac}}}{2a}\mspace{14mu}{where}}$${a = {\frac{\lambda_{0}^{2}}{d_{0}^{2}} - 1}},{b = {{\frac{2f\;\lambda_{0}}{d_{0}} - {2x^{\prime}}} = {\frac{2f\;\lambda_{0}}{d_{0}} - {2x\;\cos\;\phi}\; - {2y\; s\;{in}\;\phi}}}},{and}$c = −x^(′2) − y^(′2) = −x² − y².

FIG. 19 is an enlarged plan view of an illustrative out-coupling DOE1900 that shows the period of every 2000^(th) grating feature beingmodulated to provide for virtual image focus at 2 m. FIG. 20 is anenlarged plan view of an illustrative out-coupling DOE 2000 that showsthe period of every 2000^(th) grating feature being modulated to providefor virtual image focus at 0.5 m. The curvature of grating featuresprovides a slow period change across an out-coupling DOE to avoiddistortion in the out-coupled holographic images and the real-worldimages that are seen through the DOE and waveguide. It is emphasizedthat the virtual focus distances of 2 m and 0.5 m shown in FIGS. 19 and20 are illustrative and that various different distances for virtualimage focus may be utilized as needed to suit particular implementationrequirements.

FIG. 21 shows a side view of an illustrative assembly of threewaveguides with integrated DOEs that are stacked to form the opticalcombiner 125 (e.g., as part of the optical system 110 shown in FIG. 1and described in the accompanying text), in which each waveguide 2105,2110, and 2115 respectively handles a different color in an RGB (red,green, blue) color model within some input angular range thatcorresponds to the virtual display FOV of a given HMD device. In typicalimplementations, the red wavelength range is from 600 nm to 650 nm, thegreen wavelength range is from 500 nm to 550 nm, and the blue wavelengthrange is from 430 nm to 480 nm. Other wavelength ranges are alsopossible. An in-coupling DOE 2120, intermediate DOE 2125, andout-coupling DOE 2130 are representatively shown in FIG. 21.

The stacked waveguides 2105, 2110, and 2115 and their correspondingintegrated DOEs may be referred to collectively as a waveguide assembly2100 which functions as an optical combiner (in the discussion thatfollows, the terms are considered synonymous unless statements orcontext indicate otherwise). The color order within the assembly canvary by implementation and other color models may also be used to meetthe needs of a particular application. Use of the waveguide assemblyenables holographic images to be guided to the eye 115 across afull-color spectrum.

An inter-waveguide space (indicted by reference numeral 2150) isprovided such that the distance between adjacent waveguides of theassembly 2100 may be uniformly maintained, for example and not as alimitation, between approximately 50 micrometers (μm) and 300 μm.Structural fittings 2155 may be utilized at one or both of the top andbottom, and/or around portions of the periphery of the assembly to helpmaintain a suitable alignment of the waveguides. Typically, closespacing tolerances between the waveguides are maintained to provide theoptical combiner with performance characteristics including, forexample, color uniformity, contrast, and resolution, that meet somedesired target. While not specifically shown, spacers, supports, and/orother devices can also be utilized to provide the desired spacing amongadjacent waveguides.

In alternative implementations, assemblies with more or fewer waveguidescan be utilized, for example, for monochromatic and reduced-colorspectrum applications. A single optical substrate may be used toimplement a given waveguide in some applications, while otherapplications can use other counts. Some colors may also be supportedusing two or more waveguides. For example, an RGBG arrangement may beused in which an extra waveguide provides additional green light whichmay increase display luminance in some cases.

The waveguides 2105, 2110, and 2115 may be constructed from one oftransparent glass or plastic substrates, or combinations thereof, butthey are not limited to such materials. For example, in someimplementations, thin glass substrates providing high relativerefractive indices compared with plastic may provide a suitable balanceamong design factors including size, weight, FOV, and cost, amongothers. In other implementations, plastic waveguide substrates may meetdesign requirements more effectively when cost and weight are sought tobe optimized. In typical implementations, the DOEs disposed on thewaveguides are fabricated from plastic, for example, as molded surfacerelief gratings.

As shown, each of the DOEs are disposed on the respective waveguides2105, 2110, and 2115 in the stack to be internal to the optical combiner2100. That is, each of the DOEs is at least partially located within aninter-waveguide space 2150. Such construction ensures that none of theDOE grating structures are located on either of the external planarsurfaces 2135 and 2140 on respective eye and real-world sides of theoptical combiner. The external planar surfaces of the waveguidestherefore provide a mechanical function by protecting the DOEs duringtypical HMD handling and operation while also providing their usualoptical function in the combiner. Treatments or processes may be appliedto external planar surfaces or the substrates as a whole to furtherenhance mechanical and/or optical properties of the material in someimplementations.

FIG. 22 shows illustrative propagation of holographic image lightthrough the optical combiner 2100. For a given angular range within thevirtual FOV, light for each color component 2205, 2210, and 2215provided by the imager 105 is in-coupled into respective waveguides2115, 2110, and 2105 using respective individual in-coupling DOEs(representatively indicated by element 2120). The holographic light foreach color propagates through the respective intermediate DOEs (notshown in FIG. 22) and the waveguides in TIR and is out-coupled byrespective out-coupling DOEs (representatively indicated by element2130) to the user's eye 115 with an expanded pupil in the horizontal andvertical directions.

The in-coupling DOE 2120 for each waveguide 2105, 2110, and 2115 isconfigured to in-couple light within angular range described by the FOVand within a particular wavelength range into the waveguide. Lightoutside the wavelength range passes through the waveguide. For example,the blue holographic image light 2205 is outside the range of wavelengthsensitivity for both of the in-coupling DOEs in the red waveguide 2105and green waveguide 2110. The blue holographic image light thereforepasses through the red and green waveguides to reach the in-coupling DOEin the blue waveguide 2115 where it is in-coupled, propagated in TIRwithin the waveguide, expanded in a horizontal direction in theintermediate DOE (not shown), propagated to the out-coupling DOE whereit is expanded in a vertical direction, and out-coupled to the user'seye 115 with an expanded exit pupil relative to the input.

FIG. 23 is a flowchart 2300 of an illustrative method for providing awaveguide assembly with virtual image focus. Unless specifically stated,the methods or steps shown in the flowchart and described in theaccompanying text are not constrained to a particular order or sequence.In addition, some of the methods or steps thereof can occur or beperformed concurrently and not all the methods or steps have to beperformed in a given implementation depending on the requirements ofsuch implementation and some methods or steps may be optionallyutilized.

In step 2305 a plurality of waveguide blanks is cut from a sheet ofplanar optical substrate using a template so that each waveguide blankhas a commonly shared shape. In step 2310, an in-coupling DOE, anintermediate DOE, and a diffractive lensed out-coupling DOE are disposedon each of the plurality of the cut waveguide blanks to form arespective plurality of exit pupil expanders. The in-coupling DOE isconfigured to in-couple one or more optical beams corresponding toholographic images as an input to a respective exit pupil expander. Theintermediate DOE is configured for pupil expansion of the one or moreoptical beams in a first direction. The diffractive lensed out-couplingDOE is configured for pupil expansion of the one or more optical beamsin a second direction and is further configured to out-couple the one ormore optical beams with a predetermined focal depth as an output fromthe exit pupil expander with expanded pupil relative to the input. Thein-coupling DOE, intermediate DOE, and out-coupling DOE are eachdisposed on a common side (i.e., the same side) of the waveguide blank.

In step 2315, a stack of a plurality of exit pupil expanders is used toprovide an optical combiner, in which a number of exit pupil expandersin the stack corresponds to a number of colors utilized in the colormodel, the optical combiner having an eye side and a real-world side, inwhich the stack is formed to create at least one interior volume withinthe optical combiner and in which the exit pupil expanders are orientedin the stack to place each of the plurality of DOEs within the at leastone interior volume. As noted above, by placing the DOEs inside theoptical combiner, they are protected during handling and use of the HMDdevice in which the optical combiner is incorporated.

FIG. 24 shows an illustrative waveguide display 2400 having multipleDOEs that may be used with, or incorporated as a part of, a see-throughwaveguide 2430 to provide in-coupling, expansion of the exit pupil intwo directions, and out-coupling. The waveguide display 2400 may beutilized in an exit pupil expander that is included in the near-eyedisplay system 100 (FIG. 1) to provide holographic images to one of theuser's eyes. Each DOE is an optical element comprising a periodicstructure that can modulate various properties of light in a periodicpattern such as the direction of optical axis, optical path length, andthe like. The structure can be periodic in one dimension such asone-dimensional (1D) grating and/or be periodic in two dimensions suchas two-dimensional (2D) grating.

The waveguide display 2400 includes an in-coupling DOE 2405, anout-coupling DOE 2415, and an intermediate DOE 2410 that couples lightbetween the in-coupling and out-coupling DOEs. The in-coupling DOE isconfigured to couple image light comprising one or more imaging beamsfrom an imager 105 (FIG. 1) into the waveguide. The intermediate DOEexpands the exit pupil in a first direction along a first coordinateaxis (e.g., horizontal), and the out-coupling DOE expands the exit pupilin a second direction along a second coordinate axis (e.g., vertical)and couples light out of the waveguide to the user's eye (i.e., outwardsfrom the plane of the drawing page). The angle ρ is a rotation anglebetween the periodic lines of the in-coupling DOE and the intermediateDOE as shown. As the light propagates in the intermediate DOE(horizontally from left to right in the drawing), it is also diffracted(in the downward direction) to the out-coupling DOE.

While DOEs are shown in this illustrative example using a singlein-coupling DOE disposed to the left of the intermediate DOE 2410, whichis located above the out-coupling DOE, in some implementations, thein-coupling DOE may be centrally positioned within the waveguide and oneor more intermediate DOEs can be disposed laterally from the in-couplingDOE to enable light to propagate to the left and right while providingfor exit pupil expansion along the first direction. It may beappreciated that other numbers and arrangements of DOEs may be utilizedto meet the needs of a particular implementation.

The grating features used in the DOEs in the waveguide display 2400 maytake various suitable forms. For example, FIG. 25 shows a profile ofstraight (i.e., non-slanted) grating features 2500 (referred to asgrating bars, grating lines, or simply “gratings”), that are formed in asubstrate 2505. By comparison, FIG. 26 shows grating features 2600formed in a substrate 2605 that have an asymmetric profile. That is, thegratings may be slanted (i.e., non-orthogonal) relative to a plane ofthe waveguide. In implementations where the waveguide is non-planar,then the gratings may be slanted relative to a direction of lightpropagation in the waveguide. Asymmetric grating profiles can also beimplemented using blazed gratings, or echelette gratings, in whichgrooves are formed to create grating features with asymmetric triangularor sawtooth profiles. In FIGS. 25 and 26, the grating period isrepresented by d, the grating height by h, bar width by c, and thefilling factor by f, where f=c/d. The slanted gratings in FIG. 26 may bedescribed by slant angles α₁ and α₂.

FIGS. 27 and 28 show respective front and rear views of an illustrativeexample of a visor 2700 that incorporates an internal near-eye displaysystem that is used in a head-mounted display (HMD) device 705 worn by auser 710. The near-eye display system may be configured with a waveguideassembly with virtual image focus using the optical combiner 2100 (FIG.21) described above. The visor 2700, in some implementations, may besealed to protect the internal near-eye display system. The visor 2700typically interfaces with other components of the HMD device 705 such ashead-mounting/retention systems and other subsystems including sensors,power management, controllers, etc., as illustratively described inconjunction with FIGS. 30 and 31. Suitable interface elements (notshown) including snaps, bosses, screws and other fasteners, etc. mayalso be incorporated into the visor 2700.

The visor 2700 may include see-through front and rear shields, 2705 and2710 respectively, that can be molded using transparent materials tofacilitate unobstructed vision to the optical displays and thesurrounding real-world environment. Treatments may be applied to thefront and rear shields such as tinting, mirroring, anti-reflective,anti-fog, and other coatings, and various colors and finishes may alsobe utilized. The front and rear shields are affixed to a chassis 2705shown in the disassembled view in FIG. 29.

The sealed visor 2700 can physically protect sensitive internalcomponents, including a near-eye display system 2905 (shown in FIG. 29),when the HMD device is operated and during normal handling for cleaningand the like. The near-eye display system 2905 includes left and rightwaveguide displays 2910 and 2915 that respectively provide holographicimages to the user's left and right eyes for mixed- and/orvirtual-reality applications. The visor can also protect the near-eyedisplay system from environmental elements and damage should the HMDdevice be dropped or bumped, impacted, etc.

In some implementations, the visor can provide a measure of redundantprotection to the DOEs that are internally located within the opticalcombiner 2100 (FIG. 21), as described above when used in the near-eyedisplay system 2905. In other implementations, the visor can be reducedin size and weight such that the protection provided to the DOEs isshared between the visor and the external major surfaces of the opticalcombiner.

As shown in FIG. 28, the rear shield 2710 is configured in anergonomically suitable form 2805 to interface with the user's nose, andnose pads and/or other comfort features can be included (e.g., molded-inand/or added-on as discrete components) In some applications, the sealedvisor 2700 can also incorporate some level of optical diopter curvature(i.e., eye prescription) within the molded shields in some cases. Thesealed visor 2700 can also be configured to incorporate the lenses 1005and 1020 (FIG. 10) on either side of the near-eye display system 2905when such lenses are utilized. However, as described above in thedescription accompanying FIG. 21, such lenses can be advantageouslyeliminated from the HMD device when using the optical combiner havinginternally disposed out-coupling DOEs with integrated negative lenspower.

The present waveguide assembly with virtual image focus may be utilizedin mixed- or virtual-reality applications. FIG. 30 shows one particularillustrative example of a mixed-reality HMD device 3000, and FIG. 31shows a functional block diagram of the device 3000. The HMD device 3000provides an alternative form factor to the HMD device 705 shown in FIGS.7 and 27. HMD device 3000 comprises one or more lenses 3002 that form apart of a see-through display subsystem 3004, so that images may bedisplayed using lenses 3002 (e.g. using projection onto lenses 3002, oneor more waveguide systems, such as a near-eye display system,incorporated into the lenses 3002, and/or in any other suitable manner).

HMD device 3000 further comprises one or more outward-facing imagesensors 3006 configured to acquire images of a background scene and/orphysical environment being viewed by a user and may include one or moremicrophones 3008 configured to detect sounds, such as voice commandsfrom a user. Outward-facing image sensors 3006 may include one or moredepth sensors and/or one or more two-dimensional image sensors. Inalternative arrangements, as noted above, a mixed-reality orvirtual-reality display system, instead of incorporating a see-throughdisplay subsystem, may display mixed-reality or virtual-reality imagesthrough a viewfinder mode for an outward-facing image sensor.

The HMD device 3000 may further include a gaze detection subsystem 3010configured for detecting a direction of gaze of each eye of a user or adirection or location of focus, as described above. Gaze detectionsubsystem 3010 may be configured to determine gaze directions of each ofa user's eyes in any suitable manner. For example, in the illustrativeexample shown, a gaze detection subsystem 3010 includes one or moreglint sources 3012, such as infrared light sources, that are configuredto cause a glint of light to reflect from each eyeball of a user, andone or more image sensors 3014, such as inward-facing sensors, that areconfigured to capture an image of each eyeball of the user. Changes inthe glints from the user's eyeballs and/or a location of a user's pupil,as determined from image data gathered using the image sensor(s) 3014,may be used to determine a direction of gaze.

In addition, a location at which gaze lines projected from the user'seyes intersect the external display may be used to determine an objectat which the user is gazing (e.g. a displayed virtual object and/or realbackground object). Gaze detection subsystem 3010 may have any suitablenumber and arrangement of light sources and image sensors. In someimplementations, the gaze detection subsystem 3010 may be omitted.

The HMD device 3000 may also include additional sensors. For example,HMD device 3000 may comprise a global positioning system (GPS) subsystem3016 to allow a location of the HMD device 3000 to be determined. Thismay help to identify real-world objects, such as buildings, etc. thatmay be located in the user's adjoining physical environment.

The HMD device 3000 may further include one or more motion sensors 3018(e.g., inertial, multi-axis gyroscopic, or acceleration sensors) todetect movement and position/orientation/pose of a user's head when theuser is wearing the system as part of a mixed-reality or virtual-realityHMD device. Motion data may be used, potentially along with eye-trackingglint data and outward-facing image data, for gaze detection, as well asfor image stabilization to help correct for blur in images from theoutward-facing image sensor(s) 3006. The use of motion data may allowchanges in gaze direction to be tracked even if image data fromoutward-facing image sensor(s) 3006 cannot be resolved.

In addition, motion sensors 3018, as well as microphone(s) 3008 and gazedetection subsystem 3010, also may be employed as user input devices,such that a user may interact with the HMD device 3000 via gestures ofthe eye, neck and/or head, as well as via verbal commands in some cases.It may be understood that sensors illustrated in FIGS. 30 and 31 anddescribed in the accompanying text are included for the purpose ofexample and are not intended to be limiting in any manner, as any othersuitable sensors and/or combination of sensors may be utilized to meetthe needs of a particular implementation. For example, biometric sensors(e.g., for detecting heart and respiration rates, blood pressure, brainactivity, body temperature, etc.) or environmental sensors (e.g., fordetecting temperature, humidity, elevation, UV (ultraviolet) lightlevels, etc.) may be utilized in some implementations.

The HMD device 3000 can further include a controller 3020 such as one ormore processors having a logic subsystem 3022 and a data storagesubsystem 3024 in communication with the sensors, gaze detectionsubsystem 3010, display subsystem 3004, and/or other components througha communications subsystem 3026. The communications subsystem 3026 canalso facilitate the display system being operated in conjunction withremotely located resources, such as processing, storage, power, data,and services. That is, in some implementations, an HMD device can beoperated as part of a system that can distribute resources andcapabilities among different components and subsystems.

The storage subsystem 3024 may include instructions stored thereon thatare executable by logic subsystem 3022, for example, to receive andinterpret inputs from the sensors, to identify location and movements ofa user, to identify real objects using surface reconstruction and othertechniques, and dim/fade the display based on distance to objects so asto enable the objects to be seen by the user, among other tasks.

The HMD device 3000 is configured with one or more audio transducers3028 (e.g., speakers, earphones, etc.) so that audio can be utilized aspart of a mixed-reality or virtual-reality experience. A powermanagement subsystem 3030 may include one or more batteries 3032 and/orprotection circuit modules (PCMs) and an associated charger interface3034 and/or remote power interface for supplying power to components inthe HMD device 3000.

It may be appreciated that the HMD device 3000 is described for thepurpose of example, and thus is not meant to be limiting. It may befurther understood that the display device may include additional and/oralternative sensors, cameras, microphones, input devices, outputdevices, etc. than those shown without departing from the scope of thepresent arrangement. Additionally, the physical configuration of an HMDdevice and its various sensors and subcomponents may take a variety ofdifferent forms without departing from the scope of the presentarrangement.

As shown in FIG. 32, a waveguide assembly with virtual focus can be usedin a mobile or portable electronic device 3200, such as a mobile phone,smartphone, personal digital assistant (PDA), communicator, portableInternet appliance, hand-held computer, digital video or still camera,wearable computer, computer game device, specialized bring-to-the-eyeproduct for viewing, or other portable electronic device. As shown, theportable device 3200 includes a housing 3205 to house a communicationmodule 3210 for receiving and transmitting information from and to anexternal device, or a remote system or service (not shown).

The portable device 3200 may also include an image processor 3215 usingone or more processors for handling the received and transmittedinformation, and a virtual display system 3220 to support viewing ofimages. The virtual display system 3220 can include a micro-display oran imager 3225 configured to provide holographic images on a display3230. The image processor 3215 may be operatively connected to theimager 3225 and may obtain real-world image data, such as video datafrom a camera in the device (not shown), so that virtual- and/ormixed-reality images may be rendered on the display 3230. Inimplementations in which one or more DOEs are utilized to support thedisplay, a waveguide assembly with virtual image focus 3235 may beimplemented in accordance with the inventive principles of operationdiscussed herein.

The waveguide assembly with virtual image focus may also be utilized innon-portable devices that are configured for virtual- and/ormixed-reality applications having a display, such as gaming devices,multimedia consoles, personal computers, vending machines, smartappliances, Internet-connected devices, and home appliances, such as anoven, microwave oven and other appliances, and other non-portabledevices.

Various exemplary embodiments of the present waveguide assembly withvirtual image focus are now presented by way of illustration and not asan exhaustive list of all embodiments. An example includes a near-eyemixed-reality optical system, comprising: a see-through planar opticalwaveguide through which real-world images are viewable by a user of themixed-reality optical system, the optical waveguide including a firstplanar side and a second planar side opposite the first planar side; afirst diffractive optical element (DOE) disposed on a surface of thefirst planar side of the optical waveguide, the first DOE having aninput region and configured as an in-coupling grating to in-couple, atthe input region, one or more optical beams associated with holographicimages from a holographic image source; a second DOE disposed on asurface of the first planar side of the optical waveguide and configuredfor pupil expansion of the one or more optical beams along a firstdirection; and a third DOE disposed on a surface of the first planarside of the optical waveguide, the third DOE having an output region andconfigured for pupil expansion of the one or more optical beams along asecond direction, and further configured as an out-coupling grating toout-couple, as a display to an eye of the user, the one or more opticalbeams with expanded pupil relative to the input; wherein the third DOEprovides negative optical power using a plurality of grating featuresthat are locally modulated over an extent of the third DOE to impart aspherical wavefront to the out-coupled one or more optical beams.

In another example, the spherical wavefront has a curvature thatprovides virtual image focus for the displayed holographic images at adistance less than infinity. In another example, the virtual image focuscomprises a predetermined depth relative to the user. In anotherexample, the one or more optical beams comprise one of a red wavelengthrange, blue wavelength range, or green wavelength range. In anotherexample, the near-eye mixed-reality optical system further comprises asecond see-through planar optical waveguide and a third see-throughplanar optical waveguide, the see-through planar optical waveguidesbeing configured in a stack to form an optical combiner wherein eachsee-through planar optical waveguide propagates one or more opticalbeams for the holographic images for a different color in an RGB (red,green, blue) color model, the optical combiner having an eye side and areal-world side, wherein the second planar side of the secondsee-through planar optical waveguide forms the eye side of the combinerand the second planar side of the third see-through planar opticalwaveguide forms the real-world side of the optical combiner. In anotherexample, a uniform gap is maintained between adjacent see-through planaroptical waveguides in the stack using one of spacer or structuralfitting that is disposed along one or more peripheral edge of theoptical combiner. In another example, one or more of the see-throughplanar optical waveguides comprises a glass material.

A further example includes a head-mounted display (HMD) device wearableby a user and supporting a mixed-reality experience including full colorholographic images from a virtual world that are represented with acolor model and real-world images for objects in a real world,comprising: an imager generating one or more optical beams for theholographic images for each individual color in the color model; anoptical combiner receiving the one or more optical beams from the imageras an input and having a plurality of waveguides including a waveguidefor each individual color, in which the waveguides optically align in aplanar stack to combine the individual colors into the full colorholographic images when output from the optical combiner, wherein thestack of waveguides includes inter-waveguide spaces between adjacentwaveguides in the stack that are interior to the optical combiner; anexit pupil expander disposed on each of the waveguides for eachindividual color, the exit pupil expander comprising a plurality ofdiffractive optical elements (DOEs), in which the exit pupil expander isconfigured to provide one or more out-coupled optical beams as theoutput from the optical combiner having an expanded exit pupil relativeto the input, and in which the DOEs are located within theinter-waveguide spaces.

In another example, the plurality of DOEs in the exit pupil expanderincludes an out-coupling DOE disposed on each of the waveguides, theout-coupling DOE comprising curved grating features to provide theout-coupling DOE with negative optical power. In another example, theout-coupling DOE provides focus for the holographic images in a plane ata predetermined depth from the HMD device. In another example, theout-coupling DOE provides negative optical power to only the holographicimages that are output from the optical combiner. In another example,the exit pupil expander provides exit pupil expansion in two directions.In another example, the imager includes one of light emitting diode,liquid crystal on silicon display, organic light emitting diode array,or micro-electro mechanical system device. In another example, each ofthe waveguides and DOEs are configured as see-through. In anotherexample, the optical combiner includes three waveguides wherein aseparate waveguide is utilized for each color in a red, green, blue(RGB) color model. In another example, the plurality of DOEs comprisesan in-coupling DOE configured for in-coupling the input optical beams tothe optical combiner, an intermediate DOE configured for expanding theexit pupil in a first direction, and an out-coupling DOE configured forexpanding the exit pupil in a second direction.

A further example includes a method for assembling an optical combinerthat is associated with a color model and utilized in a mixed-realityenvironment in which holographic images are mixed with real-worldimages, comprising: cutting a plurality of waveguide blanks from a sheetof planar optical substrate using a template so that each waveguideblank has a commonly shared shape; disposing an in-coupling diffractiveoptical element (DOE), an intermediate DOE, and a diffractive lensedout-coupling DOE on each of the plurality of the cut waveguide blanks toform a respective plurality of exit pupil expanders, the in-coupling DOEconfigured to in-couple one or more optical beams corresponding toholographic images as an input to a respective exit pupil expander, theintermediate DOE configured for pupil expansion of the one or moreoptical beams in a first direction, and the diffractive lensedout-coupling DOE configured for pupil expansion of the one or moreoptical beams in a second direction and further configured to out-couplethe one or more optical beams with a predetermined focal depth as anoutput from the exit pupil expander with expanded pupil relative to theinput, in which the in-coupling DOE, intermediate DOE, and out-couplingDOE are disposed on a common side of the waveguide blank; and forming astack of a plurality of exit pupil expanders to provide an opticalcombiner, in which a number of exit pupil expanders in the stackcorresponds to a number of colors utilized in the color model, in whichthe stack is formed to create at least one interior volume within theoptical combiner, and in which the exit pupil expanders are oriented inthe stack to place each of the plurality of DOEs within the at least oneinterior volume.

In another example, the planar optical substrate comprises glass and theDOEs are fabricated from plastic. In another example, the method furtherincludes forming the stack to maintain an even gap between successiveexit pupil expanders. In another example, the even gap betweensuccessive exit pupil expanders in the stack is in range between 50 μmand 300 μm.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed:
 1. A near-eye mixed-reality optical system, comprising:a see-through planar optical waveguide through which real-world imagesare viewable by a user of the mixed-reality optical system, the opticalwaveguide including a first planar side and a second planar sideopposite the first planar side; a first diffractive optical element(DOE) disposed on a surface of the first planar side of the opticalwaveguide, the first DOE having an input region and configured as anin-coupling grating to in-couple, at the input region, one or moreoptical beams associated with holographic images from a holographicimage source; a second DOE disposed on a surface of the first planarside of the optical waveguide and configured for pupil expansion of theone or more optical beams along a first direction; and a third DOEdisposed on a surface of the first planar side of the optical waveguide,the third DOE having an output region and configured for pupil expansionof the one or more optical beams along a second direction, and furtherconfigured as an out-coupling grating to out-couple, as a display to aneye of the user, the one or more optical beams with expanded pupilrelative to the input; wherein the third DOE provides negative opticalpower using a plurality of grating features that are locally modulatedover an extent of the third DOE to impart a spherical wavefront to theout-coupled one or more optical beams.
 2. The near-eye mixed-realityoptical system of claim 1 in which the spherical wavefront has acurvature that provides virtual image focus for the displayedholographic images at a distance less than infinity.
 3. The near-eyemixed-reality optical system of claim 2 in which the virtual image focuscomprises a predetermined depth relative to the user.
 4. The near-eyemixed-reality optical system of claim 1 in which the one or more opticalbeams comprise one of a red wavelength range, blue wavelength range, orgreen wavelength range.
 5. The near-eye mixed-reality optical system ofclaim 1 further comprising a second see-through planar optical waveguideand a third see-through planar optical waveguide, the see-through planaroptical waveguides being configured in a stack to form an opticalcombiner wherein each see-through planar optical waveguide propagatesone or more optical beams for the holographic images for a differentcolor in an RGB (red, green, blue) color model, the optical combinerhaving an eye side and a real-world side, wherein the second planar sideof the second see-through planar optical waveguide forms the eye side ofthe combiner and the second planar side of the third see-through planaroptical waveguide forms the real-world side of the optical combiner. 6.The near-eye mixed-reality optical system of claim 5 in which a uniformgap is maintained between adjacent see-through planar optical waveguidesin the stack using one of spacer or structural fitting that is disposedalong one or more peripheral edge of the optical combiner.
 7. Thenear-eye mixed-reality optical system of claim 5 in which one or more ofthe see-through planar optical waveguides comprises a glass material. 8.A head-mounted display (HMD) device wearable by a user and supporting amixed-reality experience including full color holographic images from avirtual world that are represented with a color model and real-worldimages for objects in a real world, comprising: an imager generating oneor more optical beams for the holographic images for each individualcolor in the color model; an optical combiner receiving the one or moreoptical beams from the imager as an input and having a plurality ofwaveguides including a waveguide for each individual color, in which thewaveguides optically align in a planar stack to combine the individualcolors into the full color holographic images when output from theoptical combiner, wherein the stack of waveguides includesinter-waveguide spaces between adjacent waveguides in the stack that areinterior to the optical combiner; an exit pupil expander disposed oneach of the waveguides for each individual color, the exit pupilexpander comprising a plurality of diffractive optical elements (DOEs),in which the exit pupil expander is configured to provide one or moreout-coupled optical beams as the output from the optical combiner havingan expanded exit pupil relative to the input, and in which the DOEs arelocated within the inter-waveguide spaces.
 9. The HMD device of claim 8in which the plurality of DOEs in the exit pupil expander includes anout-coupling DOE disposed on each of the waveguides, the out-couplingDOE comprising curved grating features to provide the out-coupling DOEwith negative optical power.
 10. The HMD device of claim 9 in which theout-coupling DOE provides focus for the holographic images in a plane ata predetermined depth from the HMD device.
 11. The HMD device of claim 9in which the out-coupling DOE provides negative optical power to onlythe holographic images that are output from the optical combiner. 12.The HMD device of claim 8 in which the exit pupil expander provides exitpupil expansion in two directions.
 13. The HMD device of claim 8 inwhich the imager includes one of light emitting diode, liquid crystal onsilicon display, organic light emitting diode array, or micro-electromechanical system device.
 14. The HMD device of claim 8 in which each ofthe waveguides and DOEs are configured as see-through.
 15. The HMDdevice of claim 8 in which the optical combiner includes threewaveguides wherein a separate waveguide is utilized for each color in ared, green, blue (RGB) color model.
 16. The HMD device of claim 8 inwhich the plurality of DOEs comprises an in-coupling DOE configured forin-coupling the input optical beams to the optical combiner, anintermediate DOE configured for expanding the exit pupil in a firstdirection, and an out-coupling DOE configured for expanding the exitpupil in a second direction.
 17. A method for assembling an opticalcombiner that is associated with a color model and utilized in amixed-reality environment in which holographic images are mixed withreal-world images, comprising: cutting a plurality of waveguide blanksfrom a sheet of planar optical substrate using a template so that eachwaveguide blank has a commonly shared shape; disposing an in-couplingdiffractive optical element (DOE), an intermediate DOE, and adiffractive lensed out-coupling DOE on each of the plurality of the cutwaveguide blanks to form a respective plurality of exit pupil expanders,the in-coupling DOE configured to in-couple one or more optical beamscorresponding to holographic images as an input to a respective exitpupil expander, the intermediate DOE configured for pupil expansion ofthe one or more optical beams in a first direction, and the diffractivelensed out-coupling DOE configured for pupil expansion of the one ormore optical beams in a second direction and further configured toout-couple the one or more optical beams with a predetermined focaldepth as an output from the exit pupil expander with expanded pupilrelative to the input, in which the in-coupling DOE, intermediate DOE,and out-coupling DOE are disposed on a common side of the waveguideblank; and forming a stack of a plurality of exit pupil expanders toprovide an optical combiner, in which a number of exit pupil expandersin the stack corresponds to a number of colors utilized in the colormodel, in which the stack is formed to create at least one interiorvolume within the optical combiner, and in which the exit pupilexpanders are oriented in the stack to place each of the plurality ofDOEs within the at least one interior volume.
 18. The method of claim 17in which the planar optical substrate comprises glass and the DOEs arefabricated from plastic.
 19. The method of claim 17 further includingforming the stack to maintain an even gap between successive exit pupilexpanders.
 20. The method of claim 19 in which the even gap betweensuccessive exit pupil expanders in the stack is in range between 50 μmand 300 μm.